If you backup over NDMP you have to restore over NDMP so in the event of a disaster you will need another EMC device.
Also if you have mounted LUNs stored on the EMC device but attached as volumes to Windows servers, then assuming that EMC LUNs work like NetApp ones then an NDMP backup will see the LUN as a single file with no granularity inside it. To backup/restore the individual files inside the LUN you would have to use an agent for windows installed on the server that uses the LUN and not use the NDMP option.
If you jave just used the EMC device to provide CIFS shares then you will have individual file restore capability within an NDMP backup.